The present application hereby claims priority under 35 U.S.C. xc2xa7119 on German patent application number DE 10203373.0 filed Jan. 29, 2001, the entire contents of which are hereby incorporated herein by reference.
The invention generally relates to a circuit arrangement and to a method for an electronic system. In particular, it relates to a safety control system, for time-delayed outputting of a switching signal and to a method.
A circuit arrangement and a method are used, for example, as part of an emergency-off or safety circuit and/or in particular as part of a safety control system. They are used for the purpose of processing the switching signals of a safety switch or safety signal transmitter which is arranged on a protection barrier, for example on a protection door.
Depending on the respective position of the protection barrier and accordingly also on the respective switch position of the safety switch or safety signal transmitter, a system part which is arranged within the protection barrier is then immediately stopped or, in particular, is enabled with a time delay. This circuit arrangement is used in particular for moving system parts which, for example have run-on times owing to their inertia.
In detail, this means that safety parts of control systems and/or their protection devices as well as their components must be designed, constructed, selected, assembled and combined in accordance with the appropriate Standards such that they can withstand the influences to be expected.
In order to satisfy these requirements, on the one hand a majority of the control systems, systems or circuits used for safety purposes have a redundant design. Furthermore, on the other hand, functional blocks are checked at time intervals which can be specified. Until now, for this reason, safety programmable electronic controllers or systems have used two controllers. These controllers monitor one another, with duplicated components for adjustment and signal transmission.
An object of an embodiment of the present invention is to ensure safe and reliable time-delayed signal outputting, with the circuit arrangement having a simple redundant structure.
According to an embodiment of the invention, an advantageous method may be developed for computational and measurement determination of the predetermined time delay and for processing the time delay which is relevant for the outputting of the switching signal.
In comparison to a conventional circuit arrangement having two discrete timers and having in each case one actuating element whose resistance values are determined independently of one another, it is possible according to an embodiment of the invention to save one of the two actuating elements. These are costly, since they have tight component tolerances. In this case, what is now the sole actuating element is used as a common adjusting element for presetting a time delay. On the one hand, this results in a simple and hence advantageous design and simplified production of the circuit arrangement, and on the other hand it results in the reduction in the significant component tolerances.
Existing storage media and control elements can advantageously be used for storing and implementing a program.
In this case, the total resistance of the circuit arrangement, a first resistance branch as part of the first timer is determined using a method, and the second resistance branch is determined separately from the difference between the remaining and second resistance branch as part of the second timer. During a subsequent comparison, any component tolerance which may be present in the resistors in the two resistance branches can be determined in a simple manner, thus taking account of the redundant safety requirement.